1. Field of the Invention
The present invention relates to a rim-fitted tire whose weight unbalance is corrected and a method of correcting a weight unbalance of a rim-fitted tire.
2. Description of the Related Art
It is well-known that vibrations occur if a rim-fitted tire with unbalanced weight is rotated. Such a weight unbalance includes a static unbalance in which the weight is determined without rotating the rim-fitted tire and a dynamic unbalance which occurs only when the tire is rotated.
As a method of correcting such an unbalance, a method is known in which the static unbalance is first corrected, and the dynamic unbalance is then corrected by using a separate balance weight while the tire (rim-fitted tire) is being rotated. Nowadays, however, a method is mainly adopted in which the rim-fitted tire is mounted on a measuring machine (wheel balancer) and is rotated to measure the amount of unbalance requiring correction, and one balance weight is fixed at one location on each of observe and reverse rim flanges on the basis of that measurement. In this way, the static unbalance and the dynamic unbalance are corrected simultaneously (simultaneous correction method).
However, since the amount of unbalance of the rim-fitted tire is measured while the tire is being rotated on a balancer shaft above the ground, this method of simultaneously correcting the weight unbalance of the rim-fitted tire has the drawback that no consideration is given to the ground-contacting condition in which the rim-fitted tire is actually used. In addition, this weight unbalance exhibits a certain distribution in the rim-fitted tire, and it is readily conceivable that the unbalance is not concentrated on one location. When the unbalance is actually corrected, however, the unbalance is corrected by fixing one balance weight at one location on each of the obverse and reverse rim flanges.
Since this method of correction ignores the fact that the tire actually rotates in contact with the ground, as mentioned above, this method of correction cannot necessarily be said to be satisfactory.
A more specific description will be given with reference to FIG. 2. FIG. 2 is a schematic diagram showing a front elevational view and a side elevational view of the rim-fitted tire, in which the rim-fitted tire rotates on the balancer shaft, and a weight W.sub.a is fixed at a location a indicated by the balancer. Namely, this shows that a point of excessive weight lies at a location b which is radially opposite to the location a.
In a case where the tire is rotated in this state, the centrifugal forces of the rim-fitted tire are balanced. In other words, the resultant of the centrifugal forces becomes zero. Therefore, this balance does not hold when the tire is actually in contact with the ground.
FIG. 3 shows a condition in which such a tire is mounted on an actual vehicle and is in contact with the ground. That is, at the points a and b which are located on a line passing through the center of the rim, in a case where the point b side is in contact with the ground, the position of the point b changes due to the deformation of the tire during contact with the ground, so that the balance between the weight at the point b and the weight at the point a becomes unbalanced. As a result, vertical vibration (indicated by arrow A) and horizontal vibration (i.e., moment indicated by arrow B) occur in the tire.
To sum up the above-described point, it can be seen that although in accordance with the conventional balancing method the vibration can be controlled to a certain extent, a basic solution is not offered since no consideration is given to the balance in the condition in which the tire is grounded.